text:
What are the other clearance and instructions that must be read back?
The following items must always be read back:

ATC route clearances;
clearances and instructions to enter, land on, take off from, hold short of, cross or backtrack on any runway; and
runway-in-use, altimeter settings, SSR codes, level instructions, heading and speed instructions, and, whether issued by the controller or contained in Automatic Terminal Information Service (ATIS) broadcasts, transition levels.

In the definition it goes on like this: Other clearances or instructions, including conditional clearances, must be read back. What do I have to obtain from these "other clearances or instructions" I think it is the really broad term?

Side note: Please do not create extra tags just for the sake of it. [tag:radio-communications] already existed, no need to add "atcpilotcommunication" and "radiotelephony" - they're the same thing!

And what is the disturbance which I gave you my bro? :)

@VolkanEroğlu The disturbance is that you create unnecessary tags which make it much harder for other people to find the questions they are looking for. Please have a look at the tagging help page.

@Bianfable okay I will read and after that, I will write my thoughts here and thanks for attention, but nobody has a right to give a life lesson here, appropriate one is want and say kindly, thank you. I know they are same things and no time to read procedures, I'll be careful.

Actually, this is a self-policed community, so it's up to everyone to help enforce community standards, especially the community-elected moderators (notice the ♦ after @Jamiec's user name - he's a moderator) . Don't consider this an "angrily delivered life lesson", but a polite introduction into how the StackExchange communities work. It might help if you take the [tour] and read through the [help] to get a flavor of how the place works and what the expectations are.

Yeah ı agree with your opinion, but I don't agree with ''phraseology'' '' like ''unnecessary tags'', or my behaviour was remarked as a disturbance; we are learning and continue to learn. I am happy to being here and I said that I'll be careful, I don't want to be part of any discussion here, it will take us to the past. I think it is ''unnecessary'' , the necessary thing learning and teach something new each other with the border of kind and respect. Thank you, @Freeman

Lighten up cadet, this isn't a "disturbance", he's just helping you understand how this site works by kindly and respectfully pointing out redundant tags.  We all have a right to correct each other.

@MichaelHall I am cool Aged Wolf thanks and everyone has some cadet years, right? :) Okay guys, We have some misunderstanding here then, I'll be careful for next post and thanks for your advice !

I liked the "Aged Wolf" tag, I just might change my user name!  :)

My intention was to create a new tag for beginners to find some words easily; because my tags which I used in this post are used for current aviation phraseology, but my fault I didn't read the procedure. I didn't want to disrespect anyone here. With kind regards,

@VolkanEroğlu I have no idea how my reasonably polite request caused you offense, but however it did my apologies. In answer to "What's the disturbance..." - left unchecked, bad tags lead to time-consuming manual cleanup efforts. I don't get paid to do this job, and I do have a day job still.

Generally speaking, you should read back all clearances, instructions and warnings. You may in some cases not need to read back information, unless it is safety critical (for example QNH).
One of the only instructions I can think of that you do not need to read back is an instruction to report something (report passing 5000 feet, report established, report overhead XYZ). A proper reply to an instruction to report something would be "WILCO". But in all other cases, if ATC directly instructs you to do something, it should be read back.

Hey @J.Hougaard. My other question to you; transition level has to be readback, transition altitude also has to be read back? You know, transition level, layer, and altitude is a different part of airspace, and requirements are different(for example you set QNH if you descent from TL, you set QNE if you climb from TA) thanks in advance.

Transition altitude is almost always fixed (does not change). So no real reason to read it back. But since transition level changes based on QNH it can change several times a day, so it is important to read back to make sure you have the right one

Thanks @J. Hougaard

It really is overly broad. It is so for a reason. The civil aviation authorities like the FAA would like you to read back almost every instruction given to you by ATC. Some instructions they want you to read back almost verbatim. You have listed most of these instructions in your question. This is to ensure completeness and accuracy. It is the redundant step for ATC to check if their instructions were received and understood.
Remember, some nonstandard instructions may be given in a  nonstandard format. Those instructions still need to be verified. As an example, ATC has requested a number of nonstandard things of me to provide adequate spacing for slower aircraft landing ahead of me. Anything from doing right 360s on a left downwind to S-turns on final or slow flight on approach. I would either have to respond with a read back of the instructions or the word “unable”.


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What is the 'Deconfliction Service'?

High Speed Flights
2.36 - When receiving an ATS surveillance service, certain ex-military aircraft types have been granted a CAA exemption from the
  Air Navigation Order requirement to fly at an IAS less than 250 kt
  below Flight Level
  100. In order to alert the controller to this higher speed profile, pilots of exempted aircraft shall, on initial contact, prefix the
  aircraft callsign with ‘FASTJET’ or ‘FASTPROP’ (depending on
  propulsion type), e.g. “Kennington Radar, FASTJET G-ABCD request
  Deconfliction service”.
Use of this prefix shall be confined to initial contact with ATC
  agencies for periods of flight during which operations at airspeeds in
  excess of 250 kt are intended. Once acknowledged, it will not normally
  be necessary for pilots to use the prefix in subsequent transmissions
  until making initial contact with other ATSUs.

Source: Manual of Radiotelephony, Edition 2016
What is meant by Deconfliction Service?

A deconfliction service is a specific type of air traffic service.
Normally, outside of controlled airspace, air traffic controllers do not alert pilots of potential encounters with other aircraft (conflicts).
However, there my be other services offered outside of controlled airspace, typically these are Flight Information Services (FIS).
In the UK, four air traffic services are distinguished outside controlled airspace: Basic Service, Traffic Service, Deconfliction Service and Procedural Service

A Basic Service is an ATS provided for the purpose of giving advice
  and information useful for the safe and efficient conduct of flights.
  This may include weather information, changes of serviceability of
  facilities, conditions at aerodromes, general airspace activity
  information, and any other information likely to affect safety. The
  avoidance of other traffic is solely the pilot’s responsibility.

source: UK Flight Information Services CAP 774, February 2015
Note the last sentence.
The deconfliction service is defined as:

A Deconfliction Service is a surveillance based ATS where, in
  addition to the provisions of a Basic Service, the controller provides
  specific surveillance-derived traffic information and issues headings
  and/or levels aimed at achieving planned deconfliction minima, or for
  positioning and/ or sequencing. However, the avoidance of other
  traffic is ultimately the pilot’s responsibility

Again, note the last sentence.

source: Stack Exchange

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text:
Does the captain always control thrust on takeoff?
I just read an article about a day in the life of a pilot and it states "The Captain always controls the thrust in the unlikely event that the take-off needs to be aborted for safety reasons." Is this correct?
It was always my understanding that the roles of PF and PNF can be alternated between the captain and first officer, and controlling the thrust would fall into one role or the other. I also recall seeing videos of the flight engineer pushing the throttles.
If the take-off needs to be aborted, can't the captain just command the FO to "abort" or take control by saying "I have control" or similar?
Finally, will pulling back the throttles be enough to abort takeoff safely without braking? Surely it would just cause more problems?

I recently saw an old Concord video where the FE handled some of the thrust settings.

I've seen the same for the B-29.  Engineer handling engine thrust.

I believe your referenced material is mixing up "Captain" with "Pilot Flying". The person in control of the aircraft should have their hands on the throttle, Captain or not.

If the take-off needs to be aborted, can't the captain just command the FO to "abort" or take control by saying "I have control" or similar?

Having your hands on the throttles has a number of advantages:

You don't have to waste seconds (which at 200mph means about 300 feet per second)
You don't have any confusion (i.e. "What did you say?")
You don't need to discuss it with the other person (you say abort, FO says OK)

A lot of companies require both the PF and PNF's hands to be on the throttle at the same time, which has the advantages of 1) assuring that the throttle is set to its maximum power, and 2) either one can abort without having to command the other to do it. Either pilot (or the FE if they exist) have the ability to call an abort before V1, and the entire cockpit crew should follow that course without discussion until clear.

I also recall seeing videos of the flight engineer pushing the throttles.

There are also cases where if a FE is required (which usually is not the case anymore), that the FE also has their hands on the throttles along with the pilot/copilot.

Finally, will pulling back the throttles be enough to abort takeoff safely without braking? Surely it would just cause more problems?

Depending on how fast you are going, it is almost always the case that you will have to brake as well. Airplanes are pretty slick at rolling down the runway and relying on drag alone to stop you will probably result in an overrun. Usually the PF will be the one on the brakes, but the PNF may also be applying pressure just in case.

Good answer! In modern aircraft it's usual to set the autobrake system to MAX (Airbus) or RTO (Boeing) and the Spoilers into the armed position (at least for Airbus, not sure about Boeing). If set up the aircraft will brake with maximum brake power available and extend the spoilers to ensure maximum braking effieciency.

@pcfreakxx Good point, I forget about the auto-brake systems.

assuring that the throttle is set to its maximum power I thought I read in some other post somewhere on this site that maximum power is generally not used on takeoff for economic/maintenance reasons. Is that not the case?

@DavidGrinberg Depends on the airplane. In airliners, you're right that it's not normally actually maximum power, but rather a detent for "takeoff power" and what that actually means has been set up in the flight computers ahead of time for this specific takeoff (as it can vary based on temperature, humidity, runway length, aircraft weight, etc.) However, for light aircraft, it's normal to use full power on takeoff.

@DavidGrinberg reirab is correct in the above comment. Some airliners have a "Take-Off-Go-Around" button/detent which uses the calculated take-off power at the Take Off detent on the throttles. The "Go around" detent is different performs different things regarding power and autopilot.

As an addition to Ron's otherwise good answer, since I feel one aspect was left out.
Some airlines (ie. the one I work for) require the commander be in control of the thrust levers until V1 (take-off decision speed). That is because the decision to stop the take-off roll is not a light one, and the captain is the one to make the decision. And as Ron pointed out, there is no time to move hands when needed.
The control flow goes as follows (consider F/O as PF)

F/O has control of aircraft, announces "take-off"
F/O advances the levers to T/O thrust, then lets go of the thrust levers
CDR places his hand on the thrust levers
Airplane accelerates and passes V1, the CDR lets go of the thrust levers
Once airborne, the F/O takes control of the thrust levers again
If the take-off needs to be rejected, the CDR takes control of the aircraft and brings it to a stop using (auto)brakes and reverse thrust while maintaining the aircraft on runway centerline. F/O monitors and informs ATC

Regardless of who is Pilot Flying, the commander will take control of the thrust levers once the thrust is set. A First Officer acting as Pilot Flying will resume control of the thrust once the commander has removed their hand from the thrust levers at V1 AND the aircraft is airborne.
The decision to reject lies solely with the commander. As such, once the thrust is set, the First Officer as PF will have no further need to touch the thrust levers until the thrust reduction altitude. Hence the commander will cover the thrust levers in anticipation of rejecting the takeoff.

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How to correct these garbled tail numbers?
I have a collection of tail numbers of US aircraft which flew a bunch of domestic flights in the 2000's, but some of them seem to end with @ or @@, or @@@, which are obviously not a valid tail number characters. My question is - are these prefixes of tail numbers with the last character/digit removed? Or are these valid tail numbers if we just drop the @'s?
Examples:
N71@@@
N9346@
N93@@@
N795@@
N796@@
N797@@
N400@@
N401@@
N402@@
N403@@
N3744@
N405@@
N406@@
N404@@
N407@@
N3753@
N3752@
N3756@
N408@@
N409@@
N411@@
N3759@
N3765@
N3766@
N3767@
N3768@
N410@@
N412@@
N413@@
N414@@
Now, I could go look up these numbers in the registry. But - that would look up current data, while I need data from 2001 and 2002. Today, some of these numbers (when dropping the @'s) are registered to private individuals, some to non-airline companies, and some aren't registered at all.
Note: The carriers owning these specific numbers in the list above were Southwest Airlines and Delta Airlines.

Please don't use codeblocks for text that is not code. You could easily list these separated by commas, in a table, or with listing; it only makes illegible the symbols in the sentences.

Having just N71 could be a valid tail #, but airlines almost always use all 5 characters. Most likely, the "@" characters are masking the actual characters in the full tail number.
A site like PlaneSpotters dot net may help, but the search on
https://www.planespotters.net/photo/search?tag=N405
gives both 405DX (Delta) and 405WN (Southwest). Further research may reveal if either of those was only active outside your target dates, but there will probably be cases where neither can be ruled out.
In this case, the current N405DX is pretty new, while N405WN first flew in 2001 (link), so that's probably it. But there could have been a different Delta jet flying in 2001 using that registration, so again, more research required to rule that out entirely. Searching Google on the full tail number is often useful that way.
Anything with three masked characters is probably beyond resolving, but with only one or two it may be possible.

Whell, the thing is, there are counter-examples to that rule. Like this one: N3768, for Delta Airlines, issued in early 2002.

Okay, go with that then. Google those numbers with the @s removed & go with that.

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text:
Lift to drag ratio of airliners
I don't know if this is the right place to ask, but I am looking for lift-to-drag ratios (L/D) of different airliners. I have found a paper [1] which has some estimates of L/D for some jetliners, but it's a limited sample
Table 3. Estimated aerodynamic characteristics of jet airplanes (L1011, a few Boeing, Douglas and Airbus). This question also looks promising, but delivers airfoil numbers, not aircraft numbers, sadly. Is there any online resource or a place that might point me in the right direction?

[1] Historical evolution of air transport productivity and efficiency
      Rodrigo Martínez-Val, Emilio Pérez and José F. Palacín
      Universidad Politécnica de Madrid, Madrid, Spain, 28040

In a book written by the noted aerospace engineer Henk Tennekes, (The Simple Science of Flight, MIT Press, 2009) the L/D of the Boeing 777 is mentioned 'as almost 20', and the best L/D of a Boeing 747 as 18.

@xxavier - that looks like an answer to me.

In quotable literature, I recommend „Aerodynamic Design of Transport Aircraft“ by Obert. In other useful stuff, there is a very useable (but not proven by Boeing) aerodynamic model of a 787 available on the Piano X website.
I‘d add that for any really useful analysis other than level flight, getting hold of a decent engine model giving maximum and minimum (net) thrust as well as fuel flows throughout the operating range will, in my experience, prove much harder than the aerodynamics...

With regard to thrust and fuel flow, would you find some of that info in the performance section of the flight manual (assuming that is available on line)?

@Penguin True, if that’s available. That’ll get you useable takeoff, climb and probably cruise. For descent at idle thrust, engine and particularly nacelle drag is a very important factor, and it’s not always easy to even find out whether that’s wrapped into the aerodynamic model (not often the case) or the engine model; if the latter, that particular data is hard to get by as it will not be in normal aircraft or engine documentation.


text:
Can a general aviation aircraft be forced to land when crossing the airspace of a country?
I don’t know how to fly yet but my friend has a Cessna, he says it’s awesome to have and fly one and he also said he will take me for a flight one day.
I have been researching and reading online and I have a question because I’m a bit scared.
So in order to take your plane for a flight, you have to file a flight plan and when you are flying you have to, using the radio, let them know that you are on your way. Let’s say I’m flying from Italy to Germany by going over Austria and I have filled the flight plan and all the necessary paperwork.
Can the Austrians ask me to land in their country for any reason, even if I’m only going over their country to go to Germany and they have notified of this before the flight?
Will they shoot me down if I don’t comply with them and land in Austria?

Can you try to consolidate this a little?  I think this is a valid question but it is at risk of being closed or deleted as it currently is written.

I'd ask your friend about a different first flight. To fly from say Parma, Italy north to Stuttgart, Germany you have to cross some pretty high mountains, up over 12000 feet. 236nm flight, take the better part of 2 hours, or more. Check it out at www.skyvector.com, with LIMP (Parma) as your starting point and EDDS (Stuttgart) as the destination.
https://i.sstatic.net/gxLDg.jpg

As a non-pilot myself, I barely understand what SkyVector is showing me, and I've been hanging out here learning stuff for several years. I'm not really sure pointing an absolute flight newby (as the OP seems to be) to SV is particularly useful.

The map I attached shows you have some high terrain between the two countries.  Very high!  The point is flying from Italy to Germany is not an easy one. A first flight should be more of a casual sight seeing tour, not a journey over the 12000 to 14000 foot Alps, approaching the limits of how high a Cessna can go (assuming it's a single engine 172 or similar).  I crossed the Rockies here in the US, similar heights, and it took some planning to found a route where I only needed to climb to 12,500, and is not something I would not do as a casual first flight for a friend.

"you have to file a flight plan" You do for international flights (as in your question) but most flights don't need a flight plan at all.

So in order to take your plane for a flight, you have to file a flight plan and when you are flying you have to, using the radio, let them know that you are on your way.

Not necessarily. It's usually a good idea to file a flight plan for flights from point A to point B, but not all flights are like that. Quite a few flights, particularly in general aviation (GA), take off from some location, fly along some route which may or may not be predetermined, and then fly back to the original location. For those, filing a flight plan is not necessarily beneficial.
Also, a flight plan is typically only required if you will be flying under what is known as Instrument Flight Rules (IFR), or when you are flying internationally. While private pilots can get the ratings (and have the equipment) to fly IFR, I dare say that far more private flights are flown according to Visual Flight Rules, or VFR. VFR is largely similar to how you drive a car; you look out the window, avoid flying into terrain or other aircraft, and navigate by various landmarks. The only major differences are that you're working in three dimensions, and that there are far fewer road signs up at a few thousand feet above ground level and above.
For communications, both with people on the ground and with other aircraft, it's normal to use the radio for voice communications. Larger airplanes are sometimes equipped with text communications systems, similar to a fancy text messaging system on a cell phone, but I dare say very few aircraft owned by individuals are so equipped.

Let’s say I’m flying from Italy to Germany by going over Austria and I have filled the flight plan and all the necessary paperwork. Can the Austrians ask me to land in their country for any reason, even if I’m only going over their country to go to Germany and they have notified of this before the flight?

They certainly can, in principle.
About 17 years ago, there was an event in the United States which caused the grounding of all aircraft in the country all at once. It's not a completely unreasonable guess that any that didn't comply might have been dealt with by force. The US is somewhat different from the EU, being so large and having few neighboring countries, but there's no reason why something similar couldn't possibly happen in the EU. Countries have authority of their airspace, and can choose who flies through it and who doesn't, when and where.
That said, the question you should be asking is more along the lines of how likely is it? The answer to that is "very unlikely"; if you've had a flight plan approved before departure, it's very rare for it to be revoked half-way through the flight.

Will they shoot me down if I don’t comply with them and land in Austria?

Technically, they can. In practice, unless you pose an immediate threat, that is extremely unlikely to happen. Even if you do seem to pose a threat, you will be given multiple chances to sort things out before it gets close to such extreme measures.
If the Austrians do anything in such a situation, it seems more likely that they would deny you entry or require you to return to the country of origin; in your case, back past the border to Italy. Once you're back in Italian airspace, what you do is up to you and to Italian Air Traffic Control.
You might also want to check out ICAO's Manual concerning Interception of Civil Aircraft (hat tip to bogl for mentioning that one here).
But frankly, you are overthinking it. In practice, countries don't go around shooting down planes flying on filed and approved flightplans and which are in contact with air traffic control. It's unlikely that you'd even be making international flights without considerable practice, and by that time, you'd know what's expected of you in both controlled and uncontrolled airspace, and know how to comply with instructions.
If you want to fly, or even pursue a pilot's license of your own, then I encourage you to give it a try. Not everyone who tries will have what is required to get a pilot's license, but there's no way to know if you don't try. Worst case, you'll have gained a number of experiences.

So in order to take your plane for a flight, you have to file a flight plan

Usually incorrect. Flight plans are only needed for international and for IFR flights. But there are some countries where a FPLN is required for every flight, but not Italy, Austria or Germany.

when you are flying you have to, using the radio, let them know that you are on your way

Only if you've filed a Flight Plan. If you haven't, then there's no need to announce your flight.

Can the Austrians ask me to land in their country for any reason

They can, it's their country. But unless you're a criminal or a terrorist, there's probably no reason for them to actually do this.

Will they shoot me down if I don’t comply with them and land in Austria?

If they ask you to land (see above) and you don't, then they could shoot you down. It's their country and they're trying to protect it. But it hasn't happened yet.

I think things are a lot more subtle than this answer. In general, in Europe, things are not as easy as "they can do whatever they want, it's their country". For example, denying free movement of persons between Shengen member states is a definite no-go. I would be surprised if there is not a law or treaty that exactly stipulates under which conditions a private aircraft can be denied access. Also, whether or not you should announce yourself also depend on the airspace you're in.

Aviation in general is very much driven by safety. Most topics covered during training therefore directly or indirectly are intended to teach how to avoid „dying as a consequence of flying“.
There are many other hobbies where the risk of dying is much higher, I guess :)
The particular scenario you asked about is very unlikely, and there are quite a few other scenarios more plausible that have some risks associated with them. However, and that’s the important bit, risk mitigation is something that is trained right from the start, so if you’re interested, then go for it - simply make sure you get decent training, develop your competence and make safety a habit!

Excellent point. The "hobby" of driving from Italy to Germany via Austria is much more likely to get you killed in an accident than you are to be killed flying there. Especially if "shoot down" is your main point of concern.


text:
As a private, non-instrument rated pilot, can I log an instrument approach with a CFI (not a CFII) on board?
I’m a US based private pilot building time toward the instrument rating. A CFI flies with me as safety pilot for simulated instrument conditions. They are not a CFII yet. If I fly a XC under the hood and finish with a practice approach in VMC while still under the hood, can I log the approach?  I have read through FAA InFO 15012 and the approach meets all of the requirements. I understand if the safety pilot were an appropriately rated private pilot I can log the approach and follow the requirements for logging the safety pilot. Can I log the approach and log “dual received” at the same time with a non-II CFI?  If not, given where I’m at in training, would I be better off to log the approach, or log dual received, or does it even matter?  For reference, the CFI will have their II soon, I will reach XC and simulated/actual IFR minimum hour requirements, and we will begin dedicated IFR training to meet the requirements of FAR 61.65.

If you can log an instrument approach under the hood in VFR conditions with a Private Pilot in your right seat, I can see no logical reason why you shouldn't be able to with a CFI in the same seat.  And I don't see any language in the InFO link that would refute that.

Welcome to aviation.SE! If I understand correctly, you have a private certificate without an instrument rating. You’re asking if you can log training time in actual IMC with a CFI (not a CFII). Is that correct? And can you clarify what you mean by “logging an approach”? Are you asking if you can log the approach to count towards your instrument rating training as required in 61.65(c) and (d)?

You do not have an instrument rating.  There is no reason to log an approach in this situation.  I would simply log simulated instrument time and dual given.  Since you mentioned a cross country flight, the CFI cannot log XC time if he doesn't sign your logbook as dual given.  If he is only acting as a safety pilot, he would not meet the definition of cross country flight.  There are legal interpretations issued stipulating such.

@757toga You are reading the FAR incorrectly. Section (2) of that FAR requires the instructor to be a CFII. "(2) Holds an instrument rating appropriate to the aircraft used for the training on his or her flight instructor certificate..."

@757toga Your analysis of the FAR is still incorrect. Nowhere does that section talk about 15 hours of anything. The OP is asking if he can log dual towards an instrument rating when the CFI is not a CFII. He cannot, and the CFI could lose his ticket if he's caught sanctioning such behavior.

@757toga Your selective reading is getting worse. "(l) Training on control and maneuvering an aircraft solely by reference to the instruments. A flight instructor may conduct flight training on control and maneuvering an airplane solely by reference to the flight instruments, provided the flight instructor" This is NOT training leading to an instrument rating. As I said, take it up with your local FSDO, I am done with this pointless discussion.

Let us continue this discussion in chat.

As you have noted, FAR 91.109(c)(1) requires that the Safety Pilot must hold at least a private pilot certificate. The pilot certificate must have category and class ratings that are appropriate to the aircraft being flown. The safety pilot is not required to hold an instrument certificate if the flight is conducted in VFR conditions.
You can log the approach as part of the practice flight requirements, and if you have agreed so with the safety pilot you log is as PIC, but you may not, however, log the flight as "dual received" for the purpose of obtaining an instrument rating unless the Safety Pilot is in fact a CFII. "Soon" will not pass muster if you get your logs audited by the FAA.

Thank you all for the responses. This clears things up. And to clarify, all flights are in VMC. As wbeard52 states, I will log simulated instrument and dual received. There is no reason to log an approach as I am not instrument rated, and because the instructor is not CFII, it won’t count toward the 15 hours required by FAR 61.65. Again, thank you all for the responses.

Since it won't count towards your 61.65 requirements for instrument training, why log it as dual? Furthermore, it can only be logged as dual if your CFI actually signs it off. Is this non-CFII signing it off? Sounds like this person is just acting as a safety pilot, so I would just log it as if I had a, you know, safety pilot on board. Which means simulated instrument and DO log the approach and just write their name in as safety pilot. Not that you need the approach for currency, but that's the standard accepted way of logging time with a safety pilot.

@Dave-CFII 61.65 requires 40 hours of hood/actual, but only 15 must be with a CFII; the other 25 can be with a safety pilot, such as his CFIA friend.

Logging dual received is not legal in this situation unless you are logging it as dual received for something other than an instrument rating. A CFIA can only give instrument dual when they are giving basic instrument instruction for PPL as part of syllabus requirements. Again, you cannot receive dual anything towards an instrument rating from someone who is not a CFII. The only issue is deciding who logs the PIC time, you or the safety pilot, and that has to be agreed before taking off.

@757toga The FAR clearly states the requirements to be able to give instruction toward an instrument rating. The PPL syllabus is what talks about basic instrument flight training. A bare CFI can do that. This isn't rocket science, it's simple logic, but you are welcome to argue your interpretation of the regs with your local FSDO.

@757toga Any time there are two pilots at the controls, they need to agree (before engine start) who is fulfilling what roles, which dictates how they will (or won’t) log the time.

Here's what I read in 61.65D(2) A Person who applies for and instrument-airplane rating must have logged...
a). 50hrs XC time 10 must be in an airplane.
b). 40 of actual or simulated instrument time in the areas of operation listed in paragraph C of this section. 15 hrs. with a CFII.
Section C is "Flight Proficiency" and states receive instruction from an authorized Instructor in an aircraft, simulator, or FTD in accordance w/ paragraph G of this section which includes areas of operation C(1-8). Para G states up to 45 hrs XC time towards the combined Private/Instrument rating w/ an authorized instructor can be logged towards the Rating.
Yes, log the XC flight time with an instructor towards your instrument rating and the approach if all required segments were flown. The 15 hrs training must be w/a CFII. Most will need more than 15 hrs to become proficient for a Checkride. The 3 hrs in prep for the Checkride w/in 2 calendar months can be a CFI or CFII. Most stick with their CFII and include that in the 15hrs.
The 50 hrs of XC time and (40-15)= 25 hrs simulated toward the instrument rating can be logged by two appropriately rated Private Pilots sharing flight time if agreed upon PIC time. One under the hood flying by reference to instruments and the other as safety pilot in VFR. The safety pilot is required crew member under simulated instrument flight rules (91.109C). Since required if agreed upon may act as PIC and is responsible for the safety of the flight in VFR. Other wise must act as SIC. Both PIC, SIC or Safety pilot names must be written in log book entries. Seats may be swapped on return legs.

This doesn't seem to answer the stated question about logging approaches.


text:
Drain line under drag chute door of F-4 phantom
What is this drain line under the drag chute door on the F-4?

Page 2-4 of the USAF's TO 1F-4E-1, F-4E Flight Manual, describes it as a "Fuselage Cell Cavity Drain" in the pre-flight inspection checklist. It says that if you find a puddle of fuel, dripping from the drain or any evidence of recent leakage, it could mean one or more of the aircraft's fuel cells could be damaged and should be "cause for concern."
In the F-4 the fuel is stored in 7 cells at the top of the fuselage, from behind the cockpit to about the location of the exhaust, as well as wing fuel tanks, as shown in the diagram below. If any cell is leaking, the fuel will accumulate in the cavity where the cells are installed and drain out that pipe. The structure above the drain is the fuel vent mast.


text:
How do I calculate the correct rotation speed for a given density altitude?
The Airlines calculate the rotation speed of every takeoff based off the weight given to them from their operations people and also the density altitude conditions.  In General Aviation we don't perform such calculation but usually rely on the Pilot Operating Handbook (POH) recommended rotation speed.  However the POH rotation speed is based off of gross weight at sea-level and doesn't take into account high density altitudes. Is there a formula that can predict what the ideal rotation speed will be for a specific density altitude?

Won't the IAS be pretty much the same though?  Higher TAS, longer ground roll, but rotate at the same indicated?

@MichaelHall Since acceleration goes down with altitude going up, you need to rotate at a slightly higher IAS in order to be at the same IAS when the airplane leaves the ground. The difference is minuscule, though.

The given rotation speed is most often indicated air speed[IAS]. IAS is calibrated airspeed [CAS] plus instrument errors. (Outside of the airspeed guage, which as a stand alone item is usually very accurate, errors can be caused by pitot tube and static port mounting locations and large changes in angle of attack.)
CAS is a measure of dynamic pressure not true air speed. Lift is a direct function of dynamic pressure. So the required CAS for a given amount of lift is independent of the air density. If your stall speed is 50kts CAS at sea level then it will be 50kts CAS at 20,000ft.(However true airspeed will be much higher at 20,000ft.)
Airlines use, in combination with extensive performance charts; weight, air density, and temperature for calculating the true speed and thus the required auto brake settings, engine performance settings, V1 V2 Vx and Vy, and by extension determine the required length of the runway, and obstacle clearance.(All of these are determined by mass, thrust, distance, and time rather than lift alone.) Vr CAS/IAS is primarily dependent on lift.(Weight and flap settings.)
A Small aircraft POH does include charts for determining required distance of roll and 50ft obstacle clearance based on air density and maximum gross weight; many will also include selected gross weights below maximum that you can use for interpolating.
If you wish to adjust the rotation CAS based on weight[lift] the formula is the same as is used for adjusting stall speed. If needed first convert IAS to CAS using the chart in your POH, then use CAS in the following formula.
$$
S_n = S_o * \sqrt{ \frac{W_n}{ W_o} }
$$ $\text{ Where $S_o$ is original speed, $S_n$ is new speed, $W_o$ is original weight, and $W_n$ is new weight.}$
In plain text if the mathjax formula doesn't render: Sn = So*sqrt(Wn/Wo) ; speed new, speed original, weight new, weight original
After this use the chart in your POH to convert the CAS to IAS and this is your weight adjusted rotation speed.
However, it is my opinion that reducing Vr is only useful where rolling distance is the only limiting factor, because it may actually harm the distance needed to clear a 50ft obstacle. This is because as soon as you rotate you add induced drag, so acceleration before rotation is better than acceleration after rotation. The question then is about the benefit of climbing earlier at a lower initial angle[below Vx] vs later at the ideal angle[Vx for the current density].
Keep in mind that Vx is both weight and density dependent, but it is not as simple to calculate because it involves the specific aircraft design; drag, engine performance limits, and prop selection being primary variables. Mostly Vx and Vy are roughly calculated and then finalized experimentally. But you need the right instruments to accurately record climb angles and climb rates.(GPS data is simple geometry and cannot compensate for the effect of head wind or air density.)
Vx=Vy at the absolute ceiling[not "service ceiling"] for a given weight, from there Vx decreases and Vy increases as density-altitude decreases. All of the CAS numbers will decrease with decreasing weight but again precisely how much is not simple; but you may be able to interpolate existing data, and if doing experimental test pilot stuff you could extrapolate the established data in small increments.

I just want to add that transport category aircraft use a lot of automated controls like auto-brakes, auto-throttle, and an FMS which all produce much more consistent and repeatable results than the pilot of a light aircraft could manage. As such for light aircraft the variation between each takeoff roll will be greater than the difference created by doing the extra calculations. And then you have effects of runway slope, runway surface [grooved or smooth, damp, wet, snow, dry], winds, and noise abatement which are all used in the airline's computer.

Please don't put additional info in comments - include it in your answer. Comments are not always read and can get deleted. If it's only tangentially related, break it apart from the main answer by using --- or <hr> to add a horizontal rule to separate it from the main answer.


text:
What is the indicated airspeed necessary to exit ground effect on takeoff?
I always thought that a plane needed to be at stall speed or greater to be able to exit ground effect on takeoff.  However, after seeing the YouTube video in the link below I am not so sure.

In this video the winds change from a headwind to a tailwind during takeoff and the plane is not able to leave ground effect.  The pilot ultimately aborts the takeoff.  The pilot was able to achieve about 60 knots indicated airspeed while in ground effect but the plane was not able to accelerate beyond that.
Looking at the specs on the Cessna 172, which was the airplane in the video, 60 knots is the Vx speed of the Cessna 172.  So it seems like the pilot could not exit ground effect while flying at Vx?
My question is if there is a particular V speed necessary for a plane to leave ground effect or is it entirely based on acceleration and drag?

The key to getting out of Ground Effect is having sufficient amount of thrust to overcome the increase in Induced Drag as you start to move away from the ground.  If you don't have the sufficient amount of thrust to overcome the increase in induced drag you will never leave ground effect and that is indeed what happened in the video.
A few observations about the video:

The airport in the video is Big Bear Airport in California which has an elevation of 6,752 feet and you can probably bet the density altitude is much higher than the elevation.  The pilot in the video blamed the failed takeoff on a tailwind but it was most likely due to high density altitude.  A tailwind causes a considerable delay in reaching the necessary indicated airspeed for takeoff but from the video we see that the airplane stops accelerating completely at 60 knots which indicates a lack of necessary thrust.
It is a little hard to see from the video but it appears the pilot may have taken off with the mixture in the full rich position which is incorrect in high-density altitude conditions.  The correct procedure is to lean for best power before takeoff and that should really be done at any altitude including sea level.  Many pilots who learn to fly in the lowlands don't even know how to lean for best power and that may have been what happened here.  The pilot may not have been making as much power as he could have.
From the video it can been seen that some precipitation was beginning to fall.  I learned to fly at high density altitude airports (New Mexico USA) and I know from experience that high humidity greatly reduces the airplane's performance.  The amount of power that an engine can create is directly related to how much oxygen the engine can ingest at any given time.  The problem with high humidity is that the water molecules displace the oxygen molecules for a parcel of air so the oxygen percentage for that parcel is reduced.  Less oxygen means less power.  Turbocharged engines essentially force excess air into the engine and as such are much more immune to the effects of high density altitude.

As to the questions about being at Vx and still not being able to leave ground effect, that seems about right.  At the absolute ceiling of an aircraft Vx is equal to Vy and the plane will fly level at that speed.  This is essentially what happened here in the video so basically he was operating at the absolute ceiling of the aircraft at what density altitude he was at.  His absolute ceiling was probably affected by the fact that he wasn't properly leaned in this scenario.

Further complicating the situation was gusty wind, that adds drag by forcing the pilot  tosteer heavily with ailerons and (hopefully) rudder. Not sure about the mixture, it seems to me the mixture was pulled a little, full rich should not show bare metal shaft at all.

The idea that the plane was unable to leave ground effect is not quite right, in fact it's the opposite.
Ground effect results in the plane having slightly more lift (and less drag) at very low altitudes close to the ground, and it typically comes into play when your altitude is less than the wingspan of the aircraft, this is why it is sometimes described as a cushion feeling in the last moments as a plane descends down to ground level.
So for example, let's assume you are stable and approaching the runway at a constant rate of descent, lift and drag will be very much constant. Suddenly however, as you pass down to an altitude less than your wingspan, the aircraft gets a slight increase in lift, and a corresponding decrease in drag (specifically, induced drag).
As a result, your rate of descent will decrease due to the increase in lift, and your airspeed may also increase a little bit, which can give the sensation of the plane floating just as it is about to land. I personally found this a good source for understanding ground effect and induced drag:
https://www.boldmethod.com/learn-to-fly/aerodynamics/what-happens-to-your-plane-in-ground-effect-float/
Going back to the video then, the airplane is actually generating slightly more lift during the take-off roll thanks to ground effect, which essentially is helping to push the plane upwards (hence why I said it's quite the opposite above). In fact, the pilot states that he managed to gain a small amount of altitude before feeling that he had suddenly lost lift and deciding to abort, and that is likely due to primarily the weather conditions, but possibly also supplemented by the fact that he did in fact leave ground effect, and no longer had the benefit of the increased lift (and reduced drag), and hence did not have sufficient lift to sustain the initial climb, especially given the conditions.
However, I think you'd have to say that the main cause of the aborted take-off was the extreme wind conditions which did not allow them to generate sufficient airspeed required for the climb. As the pilot states, the wind changed dramatically during the take-off roll, and you can see the airspeed indicator moving around a lot too.
So in summary, changes in induced drag (which is essentially what causes ground effect) are a function of altitude vs wingspan, and is not directly related to speed.

One does not exit ground effect suddenly, ascending away from is a gradual change. Descending into it will give the gradual sensation of floatiness you described, but during a properly executed takeoff, you won't notice "an end of ground effect" .

Yes, thank you for the clarification. I think in the video the pilot does later say something along the lines of he felt a "sudden loss of lift" so I was kind of paraphrasing that whilst at the same time intending to say that he probably did indeed have marginally less lift at that point due to no longer being in ground effect. But you are entirely right, and I imagine that in reality the weather conditions were again a large contributing factor towards that sensation that he felt.

Given that the video did not mention anything being wrong with the aircraft, my money is on the shift in winds being the primary cause for the apparent reduction in airplane performance. I would also blame the pilot for rotating before he had the indicated airspeed for a climb. The time to reject a takeoff is before the wheels leave the ground.
The pilots decision to immediately land was definitely influenced by a healthy concern for the available power to overcome whatever additional unexpected weather conditions might be encountered before climbing over the obstacles beyond the end of the runway.
Looking at the video, if the aircraft was performing normally and if there were no further meteorological changes, it's very probable he would've been able to clear the obstacles. The pilot's problem in the video was uncertainty about both.
So all in all, if there is sufficient runway to land, it's definitely more prudent to do so in that kind of a situation.
As to the question of Vx and flying out of ground effect, the answer is pretty simple. As long as the aircraft stays within the envelope of conditions that allow for a climb at Vx, it'll continue to do so. But the outside world is not static and neither is engine performance.

IMO this answer best addresses the actual question of "...if there is a particular V speed necessary for a plane to leave ground effect or is it entirely based on acceleration and drag".

I propose a thought experiment to answer this question, as follows.
We fly a Cessna 172 with full fuel, baggage, and 2 passengers up to a 5000 feet cruise on a hot day, simulating ground conditions in Winslow, AZ. Now we simulate a high density-altitude takeoff roll by cutting the throttle to idle, adding backpressure to reach the verge of stall, then adding full throttle and full rich mixture and returning the elevator to neutral.
To simulate ground effect we add some flap.
With full power on, the plane then begins to accelerate and as it picks up speed it ceases to descend and instead begins to climb. We dial in some nose-down trim to simulate a takeoff roll on the ground at constant altitude and in response the plane stops climbing and gently descends as it accelerates.
We watch the VSI and airspeed and when the VSI goes positive (thus simulating the takeoff point) we rotate per the book and watch the airspeed. One or two seconds later we simulate flying out of ground effect by pulling in the flap.
To review: we are now at or near 5000' on a hot day in a loaded 172, no flaps, full power, rotated for takeoff at the book airspeed (nose up for standard climbout), and just barely out of ground effect.
In this configuration, will the plane continue to climb, stay in level flight, or stall? Imagine the plane stays in level flight. This is not what the pilot wants, so she adds some backpressure or trims nose-up to enforce the desired climb rate.
NOW: in this configuration, will the plane climb, stay in level flight, or will it stall?
In the last 10 years there have been two fatal accidents at the Winslow municipal airport where transients stopped for fuel and then crashed from low altitude just beyond the end of the runway. One was (I think) a Vari-Eze and the other a Mooney M20 series. The hypothesis in both cases was that the pilots flew out of ground effect and promptly stalled and pancaked in.
Is this plausible?

♫I was simulatin' a stall in Winslow, Arizona, such a fine day to fly♪ Nah, just doesn't have the same ring to it.

@FreeMan, you are right. Have you ever been to Wind Slow? I lived on and off there for 3 years (during which those crashes occurred) and to me, the territory resembled the surface of Mars, except for less water. -NN

Been there, bought the t-shirt. Stopped by and stood on The Corner during a trip this summer. Didn't explore town beyond that.

@FreeMan, I walked a measured 85 miles around that town during a 2-week visit and I have never seen so many smashed vodka bottles in the streets, gutters, alleyways and vacant lots as I did there. A very sad place.

If flying "out" of the ground effect was the ordeal the answers to this question make it seem like, GA fatality rates would be in a whole different order of magnitude...

but it is- at high density altitudes.


text:
What is a "fixed wing" aircraft?
I’ve been trying out different hobbies over the last year, and plane spotting is my current one.
I’ve heard some terms being thrown around about planes like the ones at the Airport - what is a Fixed Wing aircraft please?
Any examples would be good too.

Have you googled the term "fixed-wing aircraft"? Or checked wikipedia?

This does not seem to be your first account. If you have lost access to your previous one(s), you can ask them to be merged by using the contact form: https://aviation.stackexchange.com/contact

Fixed Wing is an "airplane".
Rotary Wing is a "helicopter".
The wings (lifting surface), either spin relative to the body, or are attached ("fixed") to the body.

don't forget gliders (sailplanes) --

An airplane is a type of fixed-wing aircraft, but the terms are not synonymous. See e.g. Wikipedia.

IMHO, this guy wasn't asking for the canonical definition.   He seems to want a basic understanding of the term.  For a beginner, fixed==airplane is a pretty good approximation.

Autogiros are rotary-wing aircraft, but they are not helicopters...

I think this summary is good, given the level at which the question was asked.

Fixed wing is a kind of heavier than air aircraft which uses fixed i.e. non-moving wings and other lifting services attached to the air frame and forward motion to generate lift. Examples include airplanes, gliders, powered lift aircraft, ultralights, powered parachute and weight shift controlled aircraft.
Rotary wing aircraft are heavier than air aircraft which generate lift by means of lifting surfaces attached to, and rotating about, a central shaft.  They can either be under power and driven by an engine, or auto rotating in airflow moving through the rotor disk. Examples include helicopters, gyroplanes, and powered lift.

Powered parachute is not fixed-wing. Fixed wing means rigid structure permanently attached while in flight. Parachutes are ram-air pressurised wings without rigid structure which strictly depend on flying through air to maintain their airfoil shape, and have no rigid attachment points either, rather they have suspension lines where the payload's relation to the wings changes significantly throughout the flight envelope.

@mathrick I think that’s arguable; since a powered parachute typically has no fuselage it’s not clear what the wing isn’t fixed to.  It’s reasonable to say that the aircraft is the wing, with a payload suspended below it.  What constitutes a rigid structure is open to debate, not least in high-performance paraglider design.

@Frog: it's certainly fuzzy. I suppose a parachute has more in common with a Cessna than a Eurocopter does when it comes to how the lift is generated, but it has far less in common with it than a Eurocopter when it comes to just about everything else about the craft, including how it reacts to things like turbulence. By that definition, I'm a fixed-wing aircraft when I wingsuit, and I board another fixed-wing aircraft when I deploy my parachute :)

As defined by whom, mathrick?

Re "powered parachute" -- I'd call that a "floppy wing aircraft", for sure.  Just as a pure paraglider is often called a "collapse-o-matic".  The floppy-wing concept may arguably even include conventional flex-wing hang gliders and trikes, due to their inherent reliance on shape-shifting for roll control.  Even rigid-wing hang gliders and trikes (e.g. ATOS, and trikes based on similar wings) are arguably not fixed-wing aircraft, because the wing is obviously not fixed in relation to the pilot, or to the trike body.

Um… yeah.  Wow.  First time I’ve ever heard a powered parachute referred to as a fixed wing aircraft.  I guess by that criteria an unpowered parachute is a sailplane?  Learning all kinds of new things here.

Just as a pure paraglider is often called a "collapse-o-matic"  -- kind of a riff on Cessna's "land-o-matic" concept   : )

Well there’s no Requirement that a fixed wing aircraft use a solid wing.

No, but a certain rigidity is implied in the name.  Anyway, nobody is arguing about "requirements", this is about aviation parlance. Above you asked "as defined by whom...?" Well, examples abound of fixed wing aircraft that are NOT powered parachutes, it would seem the burden of proof is on the person making the assertion.
So far it's you and whoever wrote the Wikipedia entry. And for purposes of airman certification the FAA considers them in a category of their own. I consider that fact significant.  And why the desire to even lump them with conventional fixed wing? They are SO different.

From the first two hits for Fixed:  "fastened securely in position."  "securely placed or fastened, stationary."  Kinda hard to make that claim about a loose bit of fabric don't you think?  About the only way it makes sense is if the choice is strictly binary; i.e opposite of rotary wing.  I'll stop now.  Internet debates rarely change minds.  I know mine is made up!  ;)  Cheers.

If we are to say that heavier-than-air aircraft are either fixed or rotor wing then paragliders and similar aircraft fall into the fixed wing category.  If we admit flexwing as a seperate type (which is omitted from the OP) then paragliders are clearly flexwing and we may continue to debate the taxonomy of aircraft with somewhat fixed and somewhat flexible wings.  Ultimately the definitions are set by usage, which is established by lively discussion on SE :-)

While not sourced, Wikipedia gives this definition which I agree with.  See below.

“A fixed-wing aircraft is a heavier-than-air flying machine which is capable of flight using wings that generate lift caused by the aircraft's forward airspeed and the shape of the wings. Fixed-wing aircraft are distinct from rotary-wing aircraft (in which the wings form a rotor mounted on a spinning shaft or "mast"), and ornithopters (in which the wings flap in a manner similar to that of a bird). The wings on fixed-wing aircraft aren’t necessarily rigid; kites, hang gliders, variable-sweep wing aircraft and airplanes that use wing morphing are all examples of fixed-wing aircraft.”

So yes, there are zero requirements that a fixed wing aircraft have rigid wings in order to be considered such.

But is there a reason why you feel it is useful to group things that are so incredibly dissimilar?  Because while my question about a free falling parachute being equated to a sailplane was admittedly facetious, a compelling comparison can be made.  P.S.  I happen to disagree with the Wikipedia entry so much that I might for the very first time foray into contributing rather than simply consuming information...

@Frog, Yes, "if we are to say..." or as I mentioned, if the choice is binary and we are forced to choose.  Because it definitely isn't a rotary wing.  If I had a bunch of mammals, birds, and fish and had to put them in two categories I would group the mammals and birds together because they are both air breathing.  But I would far rather group them in three distinct sets, wouldn't you?!  It just makes way more sense...

In that case, write your own answer Michael.

Will you guys give me a break...?  Sheesh!


text:
Which altimeter setting is used to define airspace boundaries?
Let's say that we're flying VFR over the top of Class D airspace at 3,000 feet. The Class D extends up to 2,900 feet - we're above it, but just barely with a 100' buffer.
We're also talking to approach control for VFR flight following. Approach has given us the QNH for their nearby Class C airport, say 29.90", which we've dutifully and correctly set into our altimeter's Kollsman window.
However, it turns out there's a strong pressure gradient today. The QNH at the Class D airport underneath us is 29.80". According to that pressure setting, our altimeter would read 100 feet lower - placing us within the upper bounds of their airspace.
In a situation like this, which pressure setting actually defines the upper boundary for the Class D airspace? Would this aircraft have inadvertently busted the Class D airspace?
(One one hand, everyone within the Class D would be using the QNH reported by the local ATIS, and would expect nearby aircraft to be participating with the Class D tower. On the other, approach control would expect you using their given altimeter setting in order to comply with cruising altitudes and for vertical separation. The only rule I can find is FAR 91.121, which just requires using an altimeter setting within 100 nautical miles.)

Airspace classes and locations are defined by regulation in 14 CFR 71, which references JO 7400.11E - Airspace Designations and Reporting Points. Here's an example of the definition of class D airspace, at KEUG (Eugene, Oregon):

ANM OR D Eugene, OR
Mahlon Sweet Field Airport, OR
(lat. 44°07'29''N., long. 123°12'43''W.)
That airspace extending upward from the surface to and including 2,900
feet MSL within a 4.6-mile radius of Mahlon Sweet Field Airport. This
Class D airspace area is effective during the specific dates and times
established in advance by a Notice to Airmen. The effective date and
time will thereafter be continuously published in the Chart
Supplement.

As you can see, the definition is given in MSL and it looks like only MSL and flight level (FL) are used in the document to indicate altitudes. MSL itself is defined in 14 CFR 1.2 as "mean sea level", which is an absolute value.
Practically speaking, in your scenario you don't need to worry about it. While on flight following, ATC is responsible for coordinating the class C/D issue. See this question and especially this answer.

"While on flight following, ATC is responsible for coordinating the class C/D issue."
My understanding is that while ATC is expected to coordinate the handoff, that doesn't relieve the pilot of the legal requirement to be in contact with the correct ATC facility before entering B/C/D airspace. If ATC fails to hand you off in time, the pilot is still considered at fault - so I'd still want to verify I'm in talking to the right facility.

@Trevor that's also my understanding from reading various discussions and FAA LOIs. ATC is expected to do something about the transition, either coordinate it on the back end or cut you loose to coordinate it yourself. But ATC failing to do what's expected isn't an ironclad defense against a pilot deviation.

Airspace boundaries are not defined by altimeter settings or Indicated Altitude. Like the field elevation, they are at True Altitude. This is defined as the actual height above the 19-year average level of the sea surface. Some boundaries are defined by the height above the surface (field elevation) which is in turn at True Altitude. The MSL vertical dimensions of the boundaries do not change based on barometric pressure or altimeter settings. They are relatively constant.
Your Indicated Altitude shown on your Altimeter may be different from the True Altitude due to barometric pressure changes, erroneous settings, or atmospheric anomalies. This does not change the boundary dimensions.
For further clarity, look at how the FAA Pilot’s Handbook of Aeronautical Knowledge defines these terms:

Types of Altitude
Altitude in itself is a relevant term only when it is specifically stated to which type of altitude a pilot is referring. Normally when the term “altitude” is used, it is referring to altitude above sea level since this is the altitude which is used to depict obstacles and airspace, as well as to separate air traffic.
Altitude is vertical distance above some point or level used as a reference. There are as many kinds of altitude as there are reference levels from which altitude is measured, and each may be used for specific reasons. Pilots are mainly concerned with five types of altitudes:

Indicated altitude—read directly from the altimeter (uncorrected) when it is set to the current altimeter setting.
True altitude—the vertical distance of the aircraft above sea level—the actual altitude. It is often expressed as feet above mean sea level (MSL). Airport, terrain, and obstacle elevations on aeronautical charts are true altitudes.

Mean sea level.
The average height of the surface of the sea at a particular location for all stages of the tide over a 19-year period.

If you are on flight following, or an IFR flight plan, it is up to the controller to clear you through an airspace or hand you off to the controller with jurisdiction. If you are not on flight following, or an IFR flight plan, don’t fly so close to the boundary without giving the local tower a courtesy call to “request” transiting their airspace at your desired altitude. It is not a bad idea to do so even if you are well above their airspace. They may know about conflicting traffic of which you are not aware.

Please add a source for your claim that vertical airspace boundaries are by default defined by height rather than altitude. I've never heard that claim before.

@expeditedescent - off the top of my head, I can think of the definitions of airspaces listed in the AIM. Specifically: 3–2–5 Class D Airspace
a. Definition. Generally, Class D airspace extends upward from the surface to 2,500 feet above the airport elevation (charted in MSL) surrounding those airports that have an operational control tower. The configuration of each Class D airspace area is individually tailored and when instrument procedures are published, the airspace will normally be designed to contain the procedures.

@expeditedescent - The PHAK uses the same verbiage to define the airspaces. The Aeronautical Chart User’s Guide defines elevation as the following: 11 ELEVATION
The highest point of an airport's usable runways measured in feet from mean sea level. When elevation is sea level it will be indicated as “00”. When elevation is below sea level a minus “-” sign will precede the figure.

So specifically for controlled airports with class D airspace in the USA it seems you are right. I think it's a bit unfair, though, to extrapolate this and claim it applies universally.

@expeditedescent - The question references Class B and Class C airports, specifically. AIM 3-2-4 has similar verbiage for Class C airspace. Class E and G towered airports in Part 91 use AGL for boundaries. So, it was not that much of a stretch to extrapolate. I have found no FAA references to the contrary. But, I am open to any you might find.

@expeditedescent - I have added citations and corrections from the PHAK, to clarify my point that the boundaries are a constant. The aircraft’s altimeter readings may fluctuate. But, the actual boundaries do not.

I guess the term "true altitude" confused me. I thought that was an FAA-translation of "height" (e.g. vertical distance above terrain). But it seems it is actually just altitude (vertical distance above sea level). Do you know why they distinguish between "true" and "indicated" altitude? What is the difference? Temperature correction?

@expeditedescent - The vertical distance above terrain or AGL is the definition of “Absolute Altitude”. The difference between Indicated Altitude and True Altitude is that True Altitude is relatively constant at a fixed amount for a fixed point. Indicated Altitude is just the reading you receive from your altimeter. Say for instance if the field altimeter setting and the actual barometric pressure do not match each other. This could be due to a rapid change in baro pressure between ATIS periods. Traffic separation is still assured with the consistent altimeter setting for all aircraft.

Let us continue this discussion in chat.

@expeditedescent - I fat-fingered the discussion button in error. Other reasons for Indicated Altitude not matching True Altitude are airfields without an available altimeter setting. Incoming/arriving aircraft can use a nearby ATIS. Or, the atmospheric conditions are not producing the expected pressures at your altitude, in your particular airmass (inconsistent or non-standard pressure lapse rate).

Which pressure setting actually defines the upper boundary for the Class D airspace?

Assuming both stations are within 100 NM, the setting from either station may be used.  If approach control assigns a setting other than the destination station, the pilot eventually must switch to the destination setting.  Whether or not approach control needs a specific setting due to unusual pressure gradient would be a matter of coordination and situation awareness.
Technically, the airspace vertical boundary would be measured by the altimeter setting directly beneath the airplane, which is just not how the airspace system works from a practical perspective.


text:
Do pilots turn off the engines during de-icing?
During winter operations and de-icing are the engines (jet engines) usually in operation? If not, what is the reason for that? Also I was wondering if the engine nacelles require de-icing since I have never seen them being spryed in any video footage.

Most jet, turboprop and reciprocating engines can be running when deicing.  There may be exceptions but I have not encountered any.  Deice fluid into the engine is wasted fluid, and is avoided.
There are four types of commonly used deicing fluids and in general they are toxic.  Ethylene glycol is the most common, and is commonly also used in automotive anti-freeze solutions, and is toxic.  For this reason, inspiration of deice fluid is avoided, which means shuttering cabin fresh air sources.  That is also why deicing is done on ramps to contain (and recover) the deice fluid, minimizing environmental impact.  The principle toxicity involves dehydration of animals as their with degradation of kidney function and the central nervous system.  Other alcohols in addition to ethylene glycol are also used, as well as corosion inhibitors, surfactants and dyes.
Engine inlets are typically heated with bleed air (some are using electric) to deice, and that not commonly done concurrently with chemical deicing. Some turboprops call for alternate induction air, using inertial/centrifugal separators to reduce the ingestion of denser particles, pieces of ice, etc.
Aircraft engines typically operate at cruise power and climb power through precipitation and while not common, sometimes turbine engines are exposed to chunks of ice being ingested.  Engines can handle a certain degree of that.  A small amount of warm, sprayed deicing fluid will not significantly harm most turbine engines. In fact some turbines tend to have icing occur on the initial compressor fans, and that ice is shed into the engine, usually without adverse consequence.
In summary, casual ingestion of deice fluid by aircraft engines is not harmful, and engines may be left running during deice operations. Engine inlet deicing is managed normally through application of bleed air.  Some turboprops will use inertial separators to reduce risks from inlet icing and icing debris.

The Fokker F28 is an exception. In 1989 Air Ontario flight 1363 crashed on takeoff due to ice. The APU was inop and there was no huffer cart available. They couldn't shut down the engines to deice and F28 does not allow deicing with the engines running.

Talking with my colleagues, there are more exceptions than I was aware of.  The F28 example is a good one.

Generally, it's not required to shut the engines down.
Sometimes you're deiced at the gate or just off the gate, and in those cases you've not started the engines yet. Or if it's necessary to remove ice on the bottom of the wings or from the bottom/front of the (extended) flaps, those would be cases when you'd shut the engines down for deicing. But most commonly, you taxi to a de-ice pad (parking area), leave the engines at idle with the bleed valves closed (to avoid getting deice fluid into the air conditioning system - even a trace of it creates kind of a stink), and deice with engines running.
The engine cowl is deiced NOT with fluid but thermally, tapping bleed air (upstream of the bleed shutoff valves, so it's always available) to heat them. Thus the fluid is not directed at the engines, but is intentionally kept away from them.


text:
What does the "blue" callout mean in the cockpit of an Airbus?
So from watching many videos in the cockpit on YouTube I have noticed that pilots will say stuff like "Loc Blue" or "2500 Blue" but what does this 'blue' mean and are there any other colours?
These images are form this video at 3:43 and 4:25.

Please include the link to the video you are referring to.

https://youtu.be/Dx7G8O6cXqk Reference to this video at 3:43 4:25

Please edit your question to include relevant information rather than use comments.  I've done this for you now.

At the top of the Primary Flight Display (PFD, the one with the artificial horizon in the center), there is a so-called Flight Mode Annunciator (FMA) with several columns indicating currently active and armed modes of flight guidance:

The first line shows active modes (in this case: SPEED, ALT, and HDG) in green color. The second line has additional information about armed modes in blue color, which will become active later, for example LOC (localizer) mode will become active instead of HDG upon localizer capture.
The callout from the pilots like "LOC blue" serves to remind themselves of the current flight guidance modes, and to maintain awareness of mode changes. This is also to ensure that their mental idea of "what the aircraft will do next" is up to date and fits to the current flight situation.
However, I'm not sure about the "2500" you mentioned.
On youtube you can find videos like this one explaining a bit more about the FMA. (screenshot taken from there). As the comment by @DeepSpace mentions, the screenshot and video mostly apply to Airbus aircraft. Other aircraft may have similar displays about flight guidance modes, but I am not aware of their specific color codings.

Might worth pointing out this answer (and question) is mostly relevant to Airbus aircraft. Also, the "2500" probably refer to LOC capture altitude.

From the caption on the 2nd photo, I'd say the "2500 blue" refers to the selected altitude on the FCU, which will show as a cyan 2500 above the PFD's altitude tape. The autopilot will descend and maintain 2500 ft, at an unspecified rate of descent ('Open descent').

Airbus uses "blue" in three different callouts, but with slightly different meaning.

"LOC blue" or "GS blue",etc, reffers to the armed modes of the F/D. It's just another way to say "localizer mode is armed and will be active once established on the signal"
"2500 blue" reffers to the altitude selection on the FCU. It specifies that 2500 feet have been selected, but blue here has a slightly different meaning: user selected altitudes are shown in blue on the PFD,  where altitude constraints from the FMGS are magenta. A similar call eg. "4000 magenta" would imply "we will stop and capture 4000' because of a constraint"
"ecam memo?" "landing no blue" reffers to the landing (or t/off) memos displayed on the ecam. Uncompleted items appear in blue, completed in greeen. "no blue" here would mean, well, no incomplete items.

So as a quick answer: "blue" term means that something is displayed in blue on the screen

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
How far from a taxiway, can a walking or biking trail be built?
How far from a small single runway airport's taxiway, can something like a walking or biking trail be built?

Depends on the size of the aircraft the airport handles, and if the airport perimeter is fenced off or not.

For one instance, there is (or was a few years ago) a nice trail from the parking area of the Alpine County (California) airport down to the Carson River.  I dare say you'll find quite a few other instance if you fly into e.g. the Idaho or Montana back country.

Very close.  GoogleEarth Kearney, AZ's airport.  The ramp has golf course access.

The taxiway can be a trail.

seeing that in places like Gibraltar major roads cross taxiways, very close indeed :)

There are airfields where paths cross the runway.

Closely related, but US-specific

ICAO recommends somewhere between 16.25 and 57.50 metres from the centreline, depending on the type of aircraft that use the taxiway (code letter A-F).
From ICAO Annex 14:

3.9.8    Recommendation.— The separation distance between the centre line of a taxiway and the centre line of a runway, the centre line of a parallel taxiway or an object should not be less than the appropriate dimension specified in Table 3-1, except that it may be permissible to operate with lower separation distances at an existing aerodrome if an aeronautical study indicates that such lower separation distances would not adversely affect the safety or significantly affect the regularity of operations of aeroplanes.

...

3.11.1    A taxiway, other than an aircraft stand taxilane, shall be included in a strip.
3.11.2    Recommendation.— A taxiway strip should extend symmetrically on each side of the centre line of the taxiway throughout the length of the taxiway to at least the distance from the centre line given in Table 3-1, column 11.

Also, there are plenty of small GA airports (in the US - I'm not that familiar with other countries) that don't have taxiways.

@jamesqf Sure, but that's not within the scope of this question

@J. Hougaard: Perfectly within scope, as it demonstrates that there's no need for an airport to have a taxiway, and nothing (in the US, anyway) to prohibit trails beside, on, or across those that do.


text:
What aircraft would have these tail numbers?
Last night I was looking at a flight radar on my phone, and I saw two blips flying close to each other over Camden, NJ. They were heading northeast at around 250 knots, and the only information displayed was their registrations, listed as 1678c37 and 1678c38. A google search of these displayed no results. Are these military or other special aircraft?

Any idea what time?

@TomMcW It was around 8:30 PM EST.

The two aircraft in question were actually only one. Apparently it was a glitch in the FR24 system. It was an Embraer ERJ-190AR, registration number N949UW on flight AA1678 from ATL to LGA.

This also pretty much validates sweber's assertion that the numbers are internal FR24 codes, because the mode-S ID is AD306E.

Thanks! I didn't think you could get archived radar data, this definitely solved it.

FR24 has archived data. I think 7 days worth for free. Subscription plans go back several months

I'm convinced this numbers were fligtradar-internal identifiers, nothing concerning the flights themselves. The following is not an answer, just what I know about flightradar data records and where to find data like yours.
The flightradar website on a computer updates its data by requesting this url, which contains coordinate bounds, filter settings and so on:
https://data-live.flightradar24.com/zones/fcgi/feed.js?bounds=40.19,39.78,-76.26,-74.03&faa=1&mlat=1&flarm=1&adsb=1&gnd=1&air=1&vehicles=1&estimated=1&maxage=7200&gliders=1&stats=1
I guess the mobile app is not different in this point.
The answer from the server is a JSON object like this:
{"full_count":14127,"version":4,
"b2fd160":["AD3C6B",39.9674,-75.9941,230,34000,368,"1306","T-MLAT2","MD88","N952DL",1475422448,"BDL","ATL","DL2457",0,0,"DAL2457",0],
"b2fe181":["A9FF54",39.9429,-75.9208,273,16860,378,"2347","T-MLAT2","B737","N743SW",1475422445,"PHL","PHX","WN601",0,1600,"SWA601",0],
"b2fc0bf":["",40.0910,-75.8714,230,39999,368,"1361","T-MLAT2","GLID","",1475422448,"","","",0,0,"GLID",0],
"b2fb3da":["A1A8DA",40.0949,-75.8623,98,8700,304,"3553","F-KPNE1","A320","N206FR",1475422446,"MKE","PHL","F91052",0,-896,"FFT1052",0]
...,
"stats":{"total":{"ads-":8655,"mlat":2916,"faa":1647,"flarm":346,"estimated":456},"visible":{"ads-b":6,"mlat":11,"faa":3,"flarm":0,"estimated":0}}
}

There is one line per aircraft, starting with a 7-digit, lowercase hex number, followed by any information about the flight in square brackets. (You can easily identify position, course, speed, registration, aircraft type and so on.)
From the structure of the file and from the fact that you can observe many subsequent hex numbers when you collect lots of data, it seems the first number is a flightradar-internal identifier, acting as counter. Whenever a new flight is detected, it gets the next number.
Within the square brackets, the first number seems to be the unique 6-digit hexadecimal (=24-bit) aircraft ID @JScarry mentioned (and the third entry, a glider, doesn't have one). But more interesting is that all data here is uppercase. (And according to this site, text messages from the aircraft like flight ID doesn't have upper/lower case)
Now, you have two subsequent, lowercase 7-digit hex numbers. This really looks like the flightradar-internal ID. So, maybe flighradar had a glitch, or it had absolutely no further information about that flights, and displayed the internal ID instead. What doesn't fit is the range, right now the numbers are about 164.000 (decimal) ahead. (EDIT: It can fit, they record 140.000-175.000 flights per day)
One can also retrieve data about flights with a certain internal ID from flightradar, but with your numbers, I get an empty record.
Yet, I think it was an internal ID, and you won't get the answer outside of flightradar.

I'd say this is an answer. The op asked about the numbers and it sounds like you have it nailed. Nice digging. +1

Aircraft equipped with  Mode S transponders transmit a unique 24 bit aircraft ID, in addition to a 4 digit transponder code (squawk). There are two ways of displaying this unique ID, as an 8 digit xxdecimalxx octal number or as a hexadecimal value. Your examples are are hexadecimal values and translate as xxx23563319xxx and xxx23563320xxx 131706067 and 131706070 in xxxdecimalxxx octal.
There is a tool at http://www.avionictools.com/icao.php to convert an aircraft registration to Mode S 24 bit ID for US and Canadian aircraft. (I checked it with mine and it works.) Different countries use different algorithms to create the ID's - some (such as Sweden) publish lists, others don't.
You can download the aircraft registration database for the USA at http://www.faa.gov/licenses_certificates/aircraft_certification/aircraft_registry/releasable_aircraft_download/
My aircraft Mode S transponder code shows up as registered to me, but neither of these show up in the list. (Per the comment, it might be because the numbers you report are not Mode S transponder codes.)
Given that the numbers are sequential and they are flying close together at a high rate of speed, I suspect that you are right that they are military.
2016-10-02 Edited to change decimal to octal. Also, all aircraft in the FAA database have Mode S transponder codes—even if they don”t have a mode S transponder.JS

24 bit addresses in hexadecimal notation are 6 characters long. The OP has 7 character identifiers, so they are surely longer than 24 bits aircraft addresses.


text:
How much does it cost the airline if an aircraft misses its take-off slot?
I was recently watching a TV programme and it said if an aircraft misses its take-off slot it will cost the airline company thousands, roughly how many thousands though???

There's no sure answer to this as it depends on too many factors which vary like airport fees, ATC service fees, number of passengers, and much more. An answerable question would be what these factors are and how they impact these costs.

and keep in mind that "thousands" is essentially nothing to an airline. it doesn't really matter how many thousands.

@sgroves If it happens once per year, that's true enough for a large airline. If it happens on a significant percentage of flights daily, however, then it's very far from nothing.

A slot time is issued for aircraft flying through busy airspaces or to busy airports where the demand (number of flights) exceeds the capacity. If 50 flights are planned to arrive at an airport in 1 hour, but the airport can only handle 40 flights per hour, then the flow of traffic needs to be regulated.
Many years ago, everyone would simply depart, and then traffic would enter airborne holdings (circling in the air) along their route as they approached their destination, until there was room to land. Obviously, this is very inefficient, since planes would use a huge amount of fuel while waiting in the air.
Air traffic flow management was introduced to reduce this. Computer systems now calculate how many flights are planned to arrive at a certain airport in a certain time span. This calculation is done many hours in advance - so early, in fact, that the majority of the affected flights have not left their departure airport yet. This has the advantage that aircraft can wait on the ground, at their departure airport, soaking up the delay they will inevitable face. They will simply not be allowed to takeoff until a time where it can be assured that there is room for them when they reach their destination.
To achieve this, aircraft are issued a takeoff slot time (CTOT - Calculated TakeOff Time), at which time the flight must depart. If the flight misses this slot time, for one reason or the other, they are not allowed to depart - instead, they must request a new slot time. If flying to a very busy airport, the new slot time could be far in the future - sometimes several hours. This means that the plane must hold on the departure airport for several hours before being able to depart.
How these CTOT times are calculated is very complex, and deserves another question if you are interested.
While there are no direct costs from missing a slot time, getting delayed will cause many indirect costs for an airline - passenger compensation for delayed and missed flights, extra pay for crew (on the plane and at the airports) and so on. So the "thousands" it may cost an airline to miss a slot time come from these indirect costs of being delayed. Obviously, the exact amount will vary greatly from flight to flight.

@J.Hougaard This is absolutely fascinating and I'd love to learn more about how all this scheduling works and the business model around that. Is there a book or publication you'd recommend?

@JohnFeminella http://www.eurocontrol.int/articles/air-traffic-flow-and-capacity-management is a good place to start, though it is pretty technical. You can find many more articles if you google 'air traffic flow management'

"planes would use a huge amount of fuel while waiting in the air" — and, in one memorable case, run out of fuel.

@MichaelSeifert True, although that was a result of many other factors as well

thanks! Also, this goes a long way toward explaining why, as a kid, I always remember circling LaGuardia (which is awesome when you're flying "to New York", and it's night, and you're a kid), to not noticing at all that I've been in a holding pattern any time in the last 10-15 years of flying. Of course, flying is now more the thing that happens between here & there than an adventure in and of itself...

@MichaelSeifert certainly more than one https://en.wikipedia.org/wiki/LaMia_Flight_2933

I'm interested in how CTOT is calculated: http://aviation.stackexchange.com/questions/35357/how-it-calculated-takeoff-time-ctot-calculated

@FreeMan It's not particularly unusual to have to hold on the way into London Heathrow, especially if the weather's not ideal; it happened to me a month ago. Perhaps you've just been lucky, or you don't fly so much at times when delays are more likely.

authors: Vladimir F Героям слава


text:
Flight Levels shall be transmitted by pronouncing each digit separately. And how should be FL200 transmitted?
It is a huge doubt I have, because I have seen on CAP 413, FL 200, transmitted as flight Level two hundred, and how should then transmit it on Europe (out of UK) and on The USA airspace?

I am fairly certain that different countries have different rules regarding this.  In European countries, I am fairly certain they use "Flight Level two hundred" where as in the United States we say "Flight Level 2-0-0".  ICAO documents will have tried to standardize this ATC phraseology but each subscribing country chooses whether or not to adopt those procedures.

Your confusion is understandable, since, back in 2016, a number of countries changed this phraseology as ICAO published the 7th edition of Annex 10. In the EU specifically, EU regulation 2016/1185 applies, which states that, generally speaking, each digit should be spoken separately, but with some exceptions:

Flight levels shall be transmitted by pronouncing each digit separately except for the case of flight levels in whole hundreds.

Example: Flight Level Two Hundred (instead of "Flight level two zero zero").

The altimeter setting shall be transmitted by pronouncing each digit separately except for the case of a setting of 1 000 hPa which shall be transmitted as “ONE THOUSAND”.

Example: QNH One Thousand (instead of "QNH one zero zero zero")

All numbers used in the transmission of transponder codes shall be transmitted by pronouncing each digit separately except that, when the transponder codes contain whole thousands only, the information shall be transmitted by pronouncing the digit in the number of thousands followed by the word “THOUSAND”

Example: Squawk seven thousand (instead of "Squawk seven zero zero zero")
Source: SKYbrary
The UK have obviously implemented this EU regulation, which is why you find the new phraseology in CAP 413.

“Flight level two zero zero”

would be standard pronunciation.
While everyone should use proper radio phraseology the system is not 100% perfect and you may hear other things on the actual radio.
The AIM provides a good example

4-2-9 Altitudes and Flight Levels
a) Up to but not including 18,000 feet
MSL, state the separate digits of the thousands plus the hundreds if
appropriate. EXAMPLE-
12,000. . . . . . . .one two thousand
12,500. . . . . . . .one two thousand five hundred
b) At and above 18,000 feet MSL (FL 180), state the
words “flight level” followed by the separate digits of the flight
level. EXAMPLE-
190. . . . . . . .Flight Level One Niner Zero
275. . . . . . . .Flight Level Two Seven Five

Maybe you should clarify that your answer only applies to the USA, since OP is asking both about the USA and about Europe

‘everyone’ without reference to what this global regulation is?

According to ICAO Annex 10 v.2-2016
8/11/18 No 91
5.2.1.4.1.2
FL 200 - flight level two hundred
FL 190 - flight level one nine zero


text:
Puzzled by description of AoA malfunction theory on recent Lion Air accident
The theory for the recent Lion Air accident states that the AoA sensor malfunctioned and the airplane systems commanded nose down.
Boeing also stated this occurs when the autopilot is disabled. The implication is that the pilots had no input to disable nose down command.
Is this inference correct in the B737-Max?

Please reword this question in a more generalized fashion so as to not tie it into an accident still under investigation. Please see this Meta question and this Meta question.

Im putting this on hold until the question is fixed - well done to the 2 answers for not entering into speculation as to the cause of this accident, however sooner or later its likely to happen! If anyone feels like rewording this question to remove references to the specific incident please flag for a moderators attention and we'll be happy to take it off hold. It is a good question aside from the accident speculation.

Your point well taken.  I will wait and educate myself before posting.  I am an ex private pilot, so will need lots of education here.  The answers were very informative.

The Operations Manual Bulletin put out by Boeing suggests that this is a trim runaway event.  Airspeed and altitude measurements are affected by the angle of attack of the airplane.  The indicated airspeed will be lower in a high angle of attack situation.  The accident airplane was reading a higher angle of attack than reality due to a malfunction of some kind.  The new avionics in the Boeing 737-MAX correct the airspeed measurement for angle of attack so airspeed was reading higher than what it should have been.  As a result the automatic trim, which is set to keep a constant airspeed, kept trying to lower the nose since the reported airspeed was too high.
The 737-MAX Operations Manual Bulletin included procedures to disable the automatic trim.  This runaway trim event occurred during the 3 flights before the accident flight but maintenance was unable to fix the problem.
More information on the accident can be found at the Aviation Herald.

From a general design perspective, an AOA sensor being involved suggests to me that they suspect the Stall Protection System fired the Stick Pusher.  When you are approaching the stall AOA, you will first get stick shaker (the vibrating doohickey on the control columns) then if it keeps increasing, the pusher will operate and shove the columns full forward, then release.
Before you get to the shaker, if the autopilot is on, the autopilot is supposed disengage itself.
There are two AOA sensors and the computers on board will generally look for agreement so if one sensor goes wonky you get some kind of fault message instead of the airplane responding as if it was stalled.
There is way more than meets the eye here.  Wait a year for the report.

The 737 does not a have stick pusher.

Roger.  Pushers are usually only installed when the stall behavior is nasty.


text:
Why do some aircraft approach the runway with a long detour and others with a short one?
I am currently analyzing flight data. For some flights landing at Frankfurt Airport.

As you can see in the graphic, some of the planes fly out about 100km to then fly again towards the runway. Some only fly out for a short distance. How can you explain that?
I assume that after the cruise phase,  the approach phase depends on factors such as traffic volume at the airport (how many want to land at my time (or in my 10min radius)) and take off?) How is the Operating direction at the airport and what kind planes want to land. Since I was told that the "plane
mix" is also relevant, for example 2x MEDIUM aircraft and 3x large.
Are there rules for such behavior? How does the ATC decide here?

Welcome to aviation.SE. I'm not really sure I understand what's going on in that picture. How did you obtain that data? the sampling rate looks a bit poor.

Hi @Federico this is flightaware Data. The samling rate is maybe poor but thats ok in that case. I would like to understand why these S/U-loops are approached. And why a flight first so far out before approach.

Closely related: https://aviation.stackexchange.com/questions/29808/why-did-this-plane-fly-in-a-zigzag-pattern and https://aviation.stackexchange.com/questions/12481/why-would-a-commercal-flight-circle-while-enroute

As you can see in this question and its answers, whether an aircraft has to go north or south is decided by ATC, as you also mention.
And, as you have correctly heard, the separation is influenced by the kind of aircraft flying in front of you, particularly during landing, as detailed in this answer.
So, in the end, an aircraft might have to fly further out if they have to put more distance between them and the preceding aircraft, or if there are more aircraft in the queue. ATC will decide in base of the currently available runways, the current amount of traffic, and whether any aircraft has declared any kind of emergency.
Note also that the approach paths for the airport are slightly asymmetrical (left side of page 11 and 12 of the pdf respectively), with ~50km on the south west approach, and ~65km on the north east one.

Hi @Frederico. Thanks for your answer. Regarding the last Document you linked. Can you please explain to me what this PDF represents? Are these the possible approach routes for Frankfurt Airport?  (What exactly do I see on page 11/12?) Where can I find information about how to read the illustrated maps?

Hi @OrgosMos. (it's FEderico, btw). Those are quite some questions and they require some extensive answers. please consider to ask them either in [chat] or as separate questions. The PDF contains the official charts of Frankfurt Airport, i.e. how aircraft can approach and leave the airspace of the airport. Information on how to read is definitely a different good question to ask.


text:
What is that CFM56 with a toothed exhaust on an A321?
I stumbled upon a wikimedia picture and I saw something that I have not seen before: a CFM56 with a toothed engine exhaust. Can someone explain to me what engine variant that is?

Source Author: Konstantin Nikiforov CC-BY-SA-3.0

Interesting picture. Welcome to Av.SE!

Usually the "teeth" are meant to reduce noise levels, up to a couple dB.

That is a very special add-on. I guess you learn something new every day.

related: https://aviation.stackexchange.com/q/19440/1467

I almost didn't upvote this question because your rep was at "172", hehe :)

The “toothed” exhaust are called Chevrons and they reduce noise. They are an option on CFM56 equipped A321 aircraft.
Wikipedia CFM International CFM56
”GE and Snecma also tested the effectiveness of chevrons on reducing jet noise. After examining configurations in the wind tunnel, CFMI chose to flight-test chevrons built into the core exhaust nozzle. The chevrons reduced jet noise by 1.3 perceived loudness decibels during takeoff conditions, and are now offered as an option with the CFM56 for the Airbus A321”


text:
TCAS II manoeuvres?
What manoeuvres does the TCAS II advise the pilot to make?
Is it RA or TA ?

The resolution advisories (RA) are the actual instructions that the TCAS system will give to the pilot.
Traffic Advisory (TA) only means the pilot needs to attempt to make visual contact and maintain visual separation if possible and prepare to respond to RA.
The actual instructions that the TCAS gives will to adjust the vertical speed, either by climbing, descending or leveling off.
There was some research conducted into adding turns into the RA however the directional antennas used by TCAS are not accurate enough to do this reliably.